code: def upgrade_outputs(outputs):
      """upgrade outputs of a code cell from v3 to v4"""
      return [upgrade_output(op) for op in outputs]
  
file_path: nbformat/nbformat/v4/convert.py
imports: from __future__ import annotations
  import json
  import re
  from traitlets.log import get_logger
  from nbformat import v3, validator
  from nbformat.corpus.words import generate_corpus_id
  from nbformat.notebooknode import NotebookNode
  from .nbbase import nbformat, nbformat_minor
label_desc: Use image node_id 9 for calling a global function with example usage: upgrade_outputs(outputs) and returns: unknown